An untreated posterior cruciate ligament (PCL) injury heals sub optimally due to laxity caused from lengthening of the PCL. Since laxity of the PCL leads to instability and injury of a person, PCL devices on the market are used to treat such injuries. These PCL devices generally use hinges that have a traditional 4-bar design, a constant force application design, or a constant resistance application design.
The traditional 4-bar design uses a hinge that attempts to closely imitate the instant center of rotation (ICoR) behavior of the biological knee. FIG. 1A illustrates moving ends of the tibia and fibula which can calculate the ICoR of the biological knee. The traditional 4-bar hinge attempts to closely imitate the movement of the biological knee. As seen in FIG. 1B, the movement of ICoR of the biological knee and traditional 4-bar hinge are both relatively stationary, moving only between 10-20 mm. This design is used to avoid device migration and/or pistoning of the device cuff.
Examples of traditional, prior art braces including traditional 4-bar hinges are found in at least: U.S. Pat. No. 4,856,501, granted Aug. 15, 1989, U.S. Pat. No. 7,044,925, granted May 16, 2006, and U.S. Pat. No. 8,048,013, granted Nov. 1, 2011, and U.S. patent application publication 2012/0059296, published Mar. 8, 2012. Each of these documents is incorporated by reference in their entirety.
A constant force design uses a passive, single axis hinge that connects a femoral cuff to the distal part of the tibial cuff. The proximal end of the tibial cuff can rotate about a pivot point on the distal cuff to allow the pushing of the tibial cuff forward by a spring independent of the movement of the hinge. However, as seen in FIG. 2, the forces exerted by the spring on the proximal tibia are constant regarding flexion angle.
A constant resistance design uses a hinge that provides dampening forces as the knee flexes, to reduce posterior tibial sag by preventing sudden rotation of the knee. However, to flex the knee joint, the patient must exert an extra flexion moment by using the hamstring muscle to load the constant resistance member of the hinge, which causes posterior tibial sag making the device counterproductive.
These known designs, however, are deficient for effectively treating a PCL injury, since these hinges do not prevent the lengthening of the PCL during flexion of the knee. The traditional 4-bar hinge design is only used to track the movement of the biological knee and is not used to provide a dynamic load to supplement the PCL. The constant force and constant resistance hinges only provide constant force and may require the patient to use muscles for leg movement that may lead to the lengthening of the PCL.
In view of these known designs, there is still a need for an orthopedic hinge that provides a dynamic load during flexion and extension of the leg to maintain anatomical alignment of the tibia and fibula to prevent the lengthening of the PCL.